1. Field of the Invention
The present invention relates to a projection display apparatus, and more particularly to a cooling device for a light valve for use in the projection display apparatus.
2. Description of the Related Art
Among the projection display apparatus, the light valve directly affects the quality of projection images, which is the most important projection optical device. Therefore, how to keep the working temperature of the light valve is important. As shown in FIG. 1, Taiwanese patent application No. 86113926 is a projection display of the prior art. The light valve 11 is fixed on the printed circuit board 12. A cooling device 13 is placed on the back surface of the printed circuit board 12 where is relative to the light valve 11. The cooling device 13 has a plurality of diffuser fins 131 which are parallel and protruding. The diffuser fins 131 conduct heat to the surrounding air for rising the air temperature to form the natural convection for heat exchange and cooling the light valve 11. The cooling device 13, by the heat buoyancy to cause the natural convection, can't actively diffuse heat so the cooling efficiency isn't good.
Referring to FIG. 2 showing another cooling device for a light valve of the prior art, a light valve 21 is fixed on a printed circuit board 23 with a fixed frame 22. A thermal diffuser 24 is placed on the back surface of the printed circuit board 23 where is relative to the light valve 21. The thermal diffuser 24 has a plurality of diffuser fins 241 which are parallel and protruding. Over the center of the diffuser fins 241 has an axial-flow fan 25. By rotating the axial-flow fan 25 to draw the air, let the air pass through the diffuser fins 241 to raise the cooling efficiency of the diffuser fins 241. However, the diffuser fins 241 of the thermal diffuser 24 is horizontally arranged, which doesn't guide the air as streamline. The axial-flow fan 25 blows the air directly to the diffuser fins 241 so that the air easily passes through the upper end of the diffuser fins 241 but can't fully exchange heat with the diffuser fins 241. Meanwhile, the airflows easily become the turbulences and loss. In addition, the central motor of the axial-flow fan 25 is arranged at the center of the cooling device 24 where is the location that the light valve 21 produces heat source. Heat can't take by the diffuser fins 241 quickly so the cooling efficiency can't raise and affect the operation quality of the light valve 21.